Extended Anderson-Grimley model for chemisorption: Solutions self-consistent within a surface complex

Publisher Website
Google Scholar
Abstract
The Anderson-type of impurity model for chemisorption by metals restricts self-consistency of charges and fields to admolecule orbitals. This paper extends such models to make them self-consistent within a "surface complex" which includes both admolecule and metal "site" orbitals. Impurity models have the virtue of not having to reconsider the entire multielectron metal for each example studied. This leads both to an economy of calculation and to an essential simplicity. Our intention is to make such models more realistic. The present model, like the Anderson model, reduces to a local "pseudomolecule" calculation requiring as inputs admolecule electronic properties and the local density of states of the bare-metal adsorption site. Solutions for the model are derived using Grimley's nonorthogonal orbital Green's functions. The surface complex local densities of states and charges are shown to be partial derivatives of simple generating functions taken with respect to elements of the one-electron Hamiltonian. The generating functions, Green's functions, and charges are derived for a useful sample problem in which the local density of states of the metal site takes a flexible functional form. Effects of image charge induced on portions of the metal outside the adsorption site in response to excess surface complex charge are also discussed. We argue that these affect the surface complex mostly by screening the Coulomb field of the excess charge. Expressions for this screened interelectronic Coulomb repulsion are derived from properties of the bare metal. The topics described above pertain to solving the model self-consistently. A subsequent paper will derive total densities of states and the change in enthalpy during chemisorption.